This proposal is a competing continuation that departs from the original research theme (cycloadditive route to aldol adducts) in significant new directions. The control of relative and absolute stereochemistry is a central focus in modern organic synthesis. Great strides have been made in stereochemical control of traditionally important transformations like aldol reactions, Diels-Alder cycloadditions, and enolate alkylations. The control of relative and absolute stereochemistry in important addition and cyclization reactions that proceed by thermal (rather than metal-promoted) pathways is less understood, and these reactions are therefore exploited less frequently. Two goals of this proposal will receive equal emphasis: 1) the development of new, stereocontrolled thermal addition and cyclization reactions, and 2) the understanding of the underlying factors that control stereochemistry. Two broad classes of reactions are targeted for study: 1) dipolar cycloadditions-where there is already a foundation on which to build, and 2) radical reactionswhere the paucity of stereocontrolled reactions and the growing importance of radicals in synthesis demand immediate study. At this early stage, the goals of the project are very fundamental (development and understanding of new reactions). However, exciting preliminary results indicate that these goals are realistic, and that original and powerful solutions to important problems in the synthesis of biomedically active compounds will be forthcoming.